Eat sufficient amounts of protein. The rule is that you need grams of protein between 1.5 times your body weights, for those who are overweight substitute your target body weight. For example, if you weigh 151 pounds, you should eat between 151 and 226 grams of protein every day if you want to consistently gain muscle. Full time bodybuilders can eat 2- 3 times their body weight in grams of protein and sometimes more, but for most of you that would be overkill.
Proteins that are perfect for building muscle include eggs.
The protein in eggs has the highest biological value. To count calorie for calorie, you need less protein from eggs than you do from other sources to achieve the same muscle building benefits. But you have to eat the yolk. Not only protein but it also contains vitamin B12 that is important for muscle contraction and fat breakdown. And eating a few eggs per day won’t increase your risk of heart disease.